JP2654004B2 - Ion implantation apparatus and method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an apparatus for implanting ions into a target substrate, and more particularly to a substantially uniform and relatively uniform dopant impurity species in a semiconductor wafer. The present invention relates to an apparatus for performing a low injection amount injection.

BACKGROUND OF THE INVENTION Ion implantation is a well-established process used today in the manufacture of solid state semiconductor devices. For example, John Wiley and Sands, Inc.
ons, Inc.) (New York 1983), a paper by SK Ghandhi, titled "VLSI Fabrication Prin.
ciples ". Further details on the ion implantation process and the equipment used therein can be found in the papers by H.Ryssel and Glawischning published by Springer-Verlag (New York 1982). Implantation
Techniques. Basically, an ion implanter scans an ion source, means for analyzing the ions of the ion source, means for accelerating the ions toward a target substrate, and an ion beam across the substrate. Means. In an ion source, the dopant species to be implanted is provided and ionized in solid, liquid, or gaseous form. Similarly, charged ions are electrostatically extracted and directed to an ion analyzer where the charged ions are separated by a magnet to produce a beam of a particular ionic species.
The ion beam emerging from the ion analyzer is again electrostatically accelerated and directed between the deflection plates of the scanning device toward the target substrate.

Usually, the target substrate is connected to ground via current measuring means known as a current integrator which measures a parameter called beam current. In order to operate in a stable state, the implanter needs to generate a certain minimum output of the ion source. This minimum output corresponds to a typical beam current minimum of about 10 ^-6 amps. Another parameter equal to the ion implantation dose is directly proportional to the beam current at the target. Effective low dose implantation requires a correspondingly low beam current. For example, during some implantation steps in certain semiconductor manufacturing processes, such as the usual threshold voltage adjustment implant in the manufacture of metal oxide semiconductor field effect transistors (MOSFETs), about 1 × 10 ^{10 to} 5 × 10 5
2.5 × 10 ^-8 so that a dose of × 10 ¹⁰ ions / cm ² can be obtained
Requires a low beam current of the order of amperes. Thus, since the ionization source produces a beam current of at least ^10-6 amps, some beam attenuator is required to achieve 2.5 x ^10-8 amps at the target.

Beam attenuating means usually take the form of a shutter that includes a "variable slit" aperture in the beam path. However, such variable slit shutters pose significant processing problems. That is, the impinging ion beam causes sputtering and electrostatic charging of the shutter material, resulting in non-uniform implantation due to beam distortion and contamination. In addition, the highly attenuated beam has a very narrow cross section, making it difficult to control its operation uniformly, but it makes the XY scan of the beam on the target critical. For example, about 1 × 10 ^{10 to} 5 × 10 ¹⁰ ions / c
The present invention was completed in the course of conducting research to solve the problems associated with the low-volume ion implantation of an amount of m ² or less.

<Summary of the Invention> An ion implantation apparatus according to the present invention includes an ion source, an ion analyzer, an ion accelerating means, and an ion deflecting means which are sequentially and continuously coupled, and a means for attenuating an ion beam. Does not use a variable slit shutter. An inert diluent gas source controllable to form a means for selecting the concentration of ions supplied to the ion analyzer by the ion source is coupled.

<Detailed Description of Preferred Embodiment> The figure shows a typical structure for an ion implantation apparatus including the configuration of the present invention. The ion implanter 10 is substantially similar to the ion implanter 10 except that a diluent gas source is shown schematically at 12 and that the variable slit beam attenuation shutter is removed or not used, as will be described in greater detail below. It is of normal design. Apparatus 10 further comprises an ion source 14 which may be of a conventional design except that it is coupled to a dilution gas source 12.
Contains.

The ion source 14 includes a supply of dopant material and means for ionizing the dopant material. The composition of the dopant is determined by the ionic species to be implanted. For example, gaseous boron trifluoride (BF ₃ ) is used for boron injection, gaseous phosphine (PH ₃ ) is usually used for phosphorus injection, and normal gas is used for arsenic injection. Arsine (AsH ₃ ) is used. The ionizing means comprises a conventional "hot filament" consisting of a filament at a first potential surrounded by a cylinder and a magnetic coil at a second potential. In operation, the filament is heated and emits electrons which strike and ionize the surrounding dopant source gas. Proper operation of the magnetic coil causes the ions generated to follow a helical trajectory, thereby further impacting and ionizing the dopant source gas.

According to the configuration of the present invention, the adjusted amount of the inert diluent gas is introduced from the diluent gas source 12 to the ion source 14, and is physically mixed with the dopant source gas surrounding the filament. The diluent gas is inert in that it does not chemically bond with the dopant source gas and is easily filtered out of the dopant species to be subsequently implanted. For example, if the dopant source gas is BF _3, nitrogen (N ₂₎ is suitable as a diluent gas. The amount of diluent gas to add is a direct function of the degree of beam attenuation required. For example, if the ion source in normal operation in the absence of the diluent gas produces a beam current of 1 × 10 ^-6 amps at the target, an implant dose equivalent to a beam current of 2.5 × 10 ^-8 amps may be generated. Desirably beam
It must be attenuated by a factor of 40 (1 × 10 ⁻⁶ /2.5×10 ⁻⁸ ). For BF ₃ dopant gas and N ₂ gas for dilution, the above conditions are by connexion achieved mixed gas consisting of 2.5% BF ₃ and 97.5% of N ₂ Prefecture.

The dopant ion species to be implanted, such as B + in the case of boron, is extracted from the ion source by a first electrode 16 located around a first accelerator tube 18. All the ions charged in the same manner, for example, if the diluent gas is nitrogen, the desired ion species as well as N ₂ + are also charged to the first accelerator
It is accelerated while passing through 18 and introduced into the ion analyzer 20 as shown.

The ion analyzer 20 has a conventional structure, and basically includes one or more magnets 22 and an ion selective aperture plate 24.
And The ion analyzer 20 magnetically bends the incoming ions by 90 °, thereby producing a spectrum of ions of different momentum impacting the ion selective aperture plate 24. The ion selective aperture plate 24 has apertures 26 that can be selectively moved to allow passage of a particular ionic species in the spectrum of ionic species striking the aperture plate 24. Thus, a beam of the selected ion species, in this example, B +, exits the ion analyzer 20. The N ₂ + ions are filtered out by the position of the ion selective aperture plate 24 and removed. Beam 28 is
At a certain distance from the analyzer 20, it is accelerated while passing through the second accelerating tube 30 by an electric potential supplied to a second electrode 32 arranged around the tube 30. The ions then pass between the conductive plates of the electrostatic deflector 34, at which time the beam is deflected in the X-Y direction before it leaves the second accelerating tube 30 and strikes the target substrate 36.

The target substrate 36 is connected to the ground via a current integrator 38 serving as a means for measuring a beam current. The amount of implanted ions, expressed in ions per square centimeter, is related to the beam current by the relationship D = It / AQe. Here, D
Is the quantity in ions / cm ² , I is the beam current in microamps, t is the exposure time in seconds,
A is the area of the scanned target in cm ² , Q
Is the charge on the implanted ionic species, e is the elementary charge constant
1.60 × 10 ^-19 coulombs.

It is called ion energy and is generally thousands or tens.
A second parameter commonly used in ion implantation processes measured at 100,000 electron volts is the first electrode 16 and the second electrode 16, typically measured at thousands or millions of volts.
Equal to the ionic charge (Q) multiplied by the accumulated potential on the electrode 32 of FIG. The ion energy determines the depth of implantation in the target substrate.

As previously mentioned, the present invention has the greatest effect when performing low volume injections. In general, an ion implanter uses three basic techniques for beam current, and hence implant volume, the current through a magnetic coil in the ion source that changes the voltage or current between the filament in the ion source and the surrounding cylinder. This is controlled by the technique of adjusting, providing a variable slit shutter between the ion analyzer and the target. However, these conventional beam current subtraction technique, there is a lot of problems when the purpose of performing the low amount injection or about 1 × 10 ¹⁰ to 5 × 10 ¹⁰ ions / cm ² following injection. Reducing the filament-to-cylinder current or voltage of the ion source, or reducing the current of the magnetic coil in the ion source, is insufficient and produces a relatively high minimum beam current. When performing low dose implants, the low beam current required may be less than the minimum that can be reliably achieved using any of the above techniques alone, and thus further variable slits Shutter must be used.

However, although variable slit shutter 40 is used in all conventional ion implanters, it has significant disadvantages. Basically, the variable slit shutter 40 has an aperture of a preselected size through which the ions must pass, thereby providing a preselected attenuation to the beam. However, the slit passage of this beam, which is necessary for low dose implants, introduces non-uniformity in the ion implantation that would otherwise traverse the plane of the target substrate. The present invention allows low volume injection and does not require a variable slit shutter. In addition, there was a significant improvement in the uniformity of the low volume injections made across the ware, and repeatable reproducibility of the resistivity as shown in the test data below.

All wafers were implanted at 100 KeV at 1.2 × 10 ¹³ ions / cm ² and baked at 1050 ° C. for about 15 minutes. The present invention is applied to the wafers 1 and 2, and the ordinary variable slit slits are applied to the wafer 3 to attenuate the ion beam.
Shrews were used. Test results cover about 8.4 cm (3.3 inches) in diameter on about 10 cm (4 inches) wafers.

The dilution gas source is set up as a normal tank of nitrogen gas connected by standard valves and regulating means to the ion source. Alternatively, a mixed gas in which an ion source gas and a dilution gas are mixed in advance, for example, a tank containing 10% BF ₃ and 90% N ₂ can be used. Therefore, the present invention can be easily applied to an existing ion implantation apparatus and implemented. Although experiments were performed using a BF ₃ ion source gas and a nitrogen diluting gas, it is expected that an ion source gas having arbitrary characteristics can be similarly diluted by this method. The diluent gas is cost-effective, non-interactive with ionic gases, stable, and easy to reduce from the dopant species by standard magnetic analysis generated in an ion analyzer. It is necessary to take into consideration the choice. The figure shown as an example illustrates a generalized configuration of an ion implanter, and the invention is not limited to an ion implanter for such a particular device.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a typical ion implantation apparatus embodying the present invention. 12 ... inert dilution gas source, 14 ... ion source, 18, 30 ...
… Ion acceleration means, 20 …… Ion analyzer, 22 ……
Deflection means (magnet).

Claims (4)

(57) [Claims] An ion source, an ion analyzer, an ion accelerating means, and a deflecting means, which are sequentially and sequentially coupled, and determine the concentration of dopant ions and diluting ions supplied to the ion analyzer by the ion source. Having a controllable inert diluent gas source coupled to the ion source to form a means for conditioning, wherein the diluent ions have a different mass than the dopant ions;
The analyzer includes an aperture plate that is selectively movable to pass the dopant ions while blocking the path of the diluting ions based on a mass difference between the ions, and the ion source includes a group consisting of boron, phosphorus, and arsenic. An ion implanter that supplies ions from the diluent gas is nitrogen. 2. The ion implanter according to claim 1, wherein the controllable inert diluent gas source comprises a tank having a valve and a regulator and containing the diluent gas. 3. A method for implanting dopant ions into a substrate using an apparatus comprising an ion source, an ion analyzer, ion acceleration means and deflection means coupled sequentially and sequentially, comprising: Introducing an inert diluent gas and a dopant gas into the ion source to adjust the concentration of ions supplied to the analyzer, ionizing the diluent gas and the dopant gas, and diluting ions and diluting ions. Generates dopant ions of different masses, orients the diluting ions and the dopant ions to the ion analyzer, and moves the movable aperture plate included in the ion analyzer based on the ion mass difference. By selectively moving the dopant ions through while blocking the path of the ion for use, An ion beam is supplied from the group consisting of boron, phosphorus and arsenic, and the diluent gas is nitrogen. A method of implanting dopant ions into a substrate. 4. The method according to claim 3, wherein the ion beam current is adjusted by adjusting an amount of a diluting gas introduced into the ion source.